Nutrition researchers in the LSU AgCenter believe a form of starch may have a greater effect on metabolism and fat deposition than other types of dietary fiber.
The LSU AgCenter research team has shown that fermentation of natural resistant starch in the large intestine is an important and previously underestimated mechanism in weight management.
The results of their most recent study will be presented next week (Jan. 14-19, 2007) in Keystone, Colo., at a symposium on diabetes and molecular genetics sponsored by the National Institutes of Health, according to Dr. Michael Keenan of the LSU AgCenter’s School of Human Ecology.
During digestion the body changes starch into sugar in the small intestine, and the sugar, which is measured in energy units called calories, is used by the body, Keenan explained. But the energy that isn’t used is stored in the body as fat, so eating more calories than the body uses leads to obesity.
When the diet has too much energy, it is stored as fat, Keenan pointed out. This comes from refined sugars, flour and fats – "calories that are cheap," he said.
Scientists know that some starches aren’t converted into sugar. They’re called resistant starches because they resist this digestion and they pass on into the large intestine, where they behave like dietary fiber.
"In addition to not being converted into sugars, resistant starches are fermented in the large intestine," Keenan said. "This process, in fact, consumes energy."
Keenan’s research team, which also includes LSU AgCenter faculty members Dr. Roy Martin, Dr. Richard Tulley and Jun Zhou and research associates Anne Raggio and Kathy McCutheon, has conducted a series of studies to "tease apart the dietary fiber effects of energy dilution of the diet from the effects of fermentation," Keenan said.
Scientists had previously assumed the major contributors of dietary fiber were bulking, which helps move wastes from the body, and energy dilution, which basically means fewer calories in a given amount of food.
"Resistant starch affects the energy density of the diet," Keenan said. "It’s like water. It has volume but produces energy for the body from digestion in the small intestine and some energy from fermentation in the large intestine. This means that the body receives significantly less energy from resistant starch compared to regular starch.
"By comparing diets matched for different variables, we were able to show that the fermentation was the mechanism with the greatest impact of the three mechanisms tested," he added.
Other research from the group has shown the dietary consumption of resistant starch significantly increased important hormones that tell the body it isn’t hungry any more and reduced abdominal fat in animal models.
"We already have shown that rats fed resistant starch have increased gut fermentation, increased intestinal expression of important peptides and decreased abdominal fat," Keenan said. "We believe the fermentation of resistant starch may be an effective, natural approach to the treatment of obesity."
The corn starch Keenan’s team is using can be added to bread and other processed foods, Keenan said. In fact, bakers are putting resistant starch in white bread in Australia to increase fiber in people’s diets.
"The advantage of the resistant starch is that it can be added to foods more readily than non-fermentable fiber," Keenan said. "Given that the fermentation effects of nondigestible resistant starch are signaling hormones that release into the blood stream, it may well be time to look further into the overall health benefits that can come from select forms of fiber."
This discovery has significant implications for weight management, because different types of fiber produce a wide range of fermentation effects.
Highly refined starches are more prone than less refined starches to be turned into sugars, because the process of refining creates smaller particles, which are easier for the body to digest.
"It’s a physical thing. Because the grain hasn’t been processed, the digesting enzymes can’t get to it," Keenan said. "The more you process it, the more you break it open, the easier the access."
Whole grains are thicker and denser, meaning they may pass into the large intestine without being totally turned to sugar. That’s one reason dietitians recommend diets high in whole grains.
While their initial studies on resistant starch have involved tests with rats, Keenan said the researchers now are going to team with scientists at the Pennington Biomedical Research Center in Baton Rouge for a short feeding study with humans.
"We have good relations between the LSU AgCenter and Pennington," Keenan said, citing in particular Susan Newman, who operates the biotechnology laboratory at Pennington. "This is an example of great collaboration between two institutions in the LSU System."
Keenan and his team’s research has been funded in part by the National Starch and Chemical Co., which manufactures the corn starch used in the study. They also recently received a grant from the National Institutes of Health to fund additional work.
"To validate effects of fermentation is most important," Keenan said.
Keenan said the results of this research may affect cancer, heart disease and diabetes, which are all associated with obesity.
"It’s bigger than we once thought," he said of the potential effects of adding resistant starch to people’s diets. "A lot of research is being done.
"It’s a real crisis," he added. "Something big has to happen, because obesity is such a growing problem."
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